Hidden Trigger for the Giant Starburst Arc in M83?

The huge star formation events that occur at some galactic centers do notprovide enough clues as to their origin, since the morphological signatures ofthe triggering mechanism are smeared out in the timescale of a few orbitalrevolutions of the galaxy core. Our high spatial resolution three-dimensionalnear-infrared spectroscopy for the first time reveals that a previously knownhidden mass concentration is located exactly at the youngest end of a giantstar-forming arc. This location, the inferred average cluster ages, and thedynamical times clearly indicate that the interloper has left behind a spur ofviolent star formation in M 83, in a transient event lasting less than oneorbital revolution. The study of the origin (bar funneling or cannibalizedsatellite) and fate (black hole merging or giant stellar cluster) of thissystem could provide clues to the question of core growing and morphologicalevolution in grand-design spiral galaxies. In particular, our TreeSPH numericalmodeling suggests that the two nuclei could coalesce, forming a single massivecore in about 60 million years or less.Comment: 18 pages, including 4 figures (3 in color). The Astrophysical Journal, in pres